Conventionally, as a method of forming an image given a stereoscopic effect in the commercial printing field, there is, for example, a so-called barco printing method which increases a thickness of a printed ink layer or of a transparent varnish layer in an image to form a rugged printed image, thereby giving a stereoscopic effect to the printed image. Particularly, a thick transparent varnish layer exhibits a lens effect to an image of an under layer, whereby a good stereoscopic effect is given to the image.
Further, there has been realized a so-called lenticular printing method in which a semicircular convex lens sheet is laminated on an image to give a 3D effect to the image.
In recent years, in the commercial printing field, a POD (print on demand) apparatus according to an electrophotographic process, which can provide a small volume of prints according to a plateless printing process at a short period and at low cost, has been widely applied. It is required also in such a POD apparatus to realize an image with a stereoscopic appearance. In order to meet such a requirement, there is proposed, for example, a technique which forms a stereo image by forming a texture pattern on an image employing clear toner (see, for example, Japanese Patent O.P.I. Publication No. 2008-532066).
Further, there is proposed a technique which expands a toner image formed employing toner containing a foaming agent. As a technique to apply such a technique, there is a technique disclosed for example in Japanese Patent O.P.I. Publication No. 2007-93699 in which a stereo image is formed employing clear toner or white toner. Furthermore, there is proposed a method disclosed on the Internet (searched on Apr. 1, 2009)<URL: http://japan.zdnet.com/news/hardware/story/0,2000056184,20350441,00.htm> in which a stereo image is formed by adding a foaming agent to an image support medium itself.
However, the methods described above do not give a sufficient stereoscopic effect to an image, although they can form a thick and stereoscopic clear toner layer. For example, in a method of utilizing a texture pattern, a clear toner for forming the texture pattern is expanded by application of pressure and heat due to contact heating. In a method of utilizing a clear toner containing a foaming agent, clearness of an image is lowered by a gas bubble generated within the clear toner. In a method of utilizing an image support medium containing a foaming agent, the image support medium itself elevates, but a toner image does not take a stereoscopic structure, and therefore a stereoscopic effect cannot be given to the image.